Bistable Gradient Networks II: Storage Capacity and Behaviour Near Saturation

We examine numerically the storage capacity and the behaviour near saturation of an attractor neural network consisting of bistable elements with an adjustable coupling strength, the Bistable Gradient Network (BGN). For strong coupling, we find evidence of a first-order "memory blackout" phase transition as in the Hopfield network. For weak coupling, on the other hand, there is no evidence of such a transition and memorized patterns can be stable even at high levels of loading. The enhanced storage capacity comes, however, at the cost of imperfect retrieval of the patterns from corrupted versions.Comment: 15 pages, 12 eps figures. Submitted to Phys. Rev. E. Sequel to cond-mat/020356

Numerical continuation methods: a perspective

AbstractIn this historical perspective the principal numerical approaches to continuation methods are outlined in the framework of the mathematical sources that contributed to their development, notably homotopy and degree theory, simplicial complexes and mappings, submanifolds defined by submersions, and singularity and foldpoint theory

Coronary lumen at six-month follow-up of a new radiopaque Cordis tantalum stent using quantitative angiography and intracoronary ultrasound.

To determine the reliability of geometric (edge-detection) quantitative coronary angiographic analysis (QCA) of restenosis within a new Cordis tantalum stent, QCA and intracoronary ultrasound (ICUS) measurements were compared in both an experimental restenosis model and in the clinical follow-up of patients. In the experimental series, Plexiglas phantom vessels with concentric stenosis channels ranging from 0.75 to 3.0 mm in diameter and with a reference diameter of 3.0 mm were imaged both before and after their insertion in tantalum stents. In the clinical series, the agreement of QCA and ICUS measurements were studied in 23 patients who had undergone coronary implantation of the new tantalum stent and in 23 patients who had undergone balloon angioplasty 6 months previously. The reliability of QCA declined in the presence of the radiopaque stent (accuracy of QCA decreased from -0.07 to -0.12 mm), whereas the reliability of lumen measurements by ICUS was independent of the presence of the radiopaque stent (-0.12 and -0.13 mm). Without the stent, the average minimal luminal diameter (MLD) obtained by QCA of the 1.00 mm Plexiglas vessel was 1.00 +/- 0.01 mm, and the 3.00 mm reference vessel diameter was 2.81 +/- 0.05 mm, providing a 64 +/- 1% diameter stenosis. After introduction of the stent, the average MLD and reference vessel diameter were 0.99 +/- 0.06 and 3.36 +/- 0.17 mm, respectively, providing a diameter stenosis of 71 +/- 2%. ICUS measurements (2.77 mm) of the reference vessel diameter (3.00 mm) were unaffected by the presence of the stent. (ABSTRACT TRUNCATED AT 250 WORDS

Excimer laser coronary angioplasty in the Netherlands: preamble for a randomized study

The immediate outcome of ELCA by XeCl excimer laser radiation is described in 53 patients who were selected to undergo ELCA from December 1990 to September 1991 in two centers that are currently performing ELCA in the Netherlands. Immediate success rates on the basis of visual assessment of the angiogram were as follows. Laser success (> 20% reduction of diameter stenosis after ELCA alone) was observed in 77% of patients, procedural success (< 50% residual stenosis after ELCA with or without adjunctive balloon dilatation [PTCA]) in 91%, and clinical success (procedural success without clinical complications) in 83% of patients. Quantitative coronary angiography by automated contour detection was performed in 31 patients who underwent ELCA in the Thoraxcenter. The minimal luminal diameter (mean +/- SD) of the treated coronary segments increased from 0.77 +/- 0.41 mm to 1.24 +/- 0.25 mm after ELCA and further to 1.67 +/- 0.29 mm after adjunctive PTCA in 25 patients. The present experience is put in perspective of results initially reported by other centers and compared with data from multicenter registries of ELCA. Finally, a short description is given of the design of a prospective, randomized trial of ELCA versus conventional PTCA (AMRO trial)

Selective protein unfolding: a universal mechanism of action for the development of irreversible inhibitors

High-throughput differential scanning fluorimetry of GFP-tagged proteins (HT-DSF-GTP) was applied for the identification of novel enzyme inhibitors acting by a mechanism termed: selective protein unfolding (SPU). Four different protein targets were interrogated with the same library to identify target-selective hits. Several hits selectively destabilized bacterial biotin protein ligase. Structure–activity relationship data confirmed a structure-dependent mechanism of protein unfolding. Simvastatin and altenusin were confirmed to irreversibly inactivate biotin protein ligase. The principle of SPU combined with HT-DSF-GTP affords an invaluable and innovative workflow for the identification of new inhibitors with potential applications as antimicrobials and other biocides

Delineation of the ancestral tus-dependent replication fork trap

In Escherichia coli, DNA replication termination is orchestrated by two clusters of Ter sites forming a DNA replication fork trap when bound by Tus proteins. The formation of a ‘locked’ Tus– Ter complex is essential for halting incoming DNA replication forks. However, the absence of replication fork arrest at some Ter sites raised questions about their significance. In this study, we examined the genome-wide distribution of Tus and found that only the six innermost Ter sites (TerA–E and G) were significantly bound by Tus. We also found that a single ectopic insertion of TerB in its non-permissive orientation could not be achieved, advocating against a need for ‘back-up’ Ter sites. Finally, examination of the genomes of a variety of Enterobacterales revealed a new replication fork trap architecture mostly found outside the Enterobacteriaceae family. Taken together, our data enabled the delineation of a narrow ancestral Tus-dependent DNA replication fork trap consisting of only two Ter sites